docs: def _extract_vararray_max(tform):
      """
      Extract number from PX(number)
      """
      first = tform.find('(')
      last = tform.rfind(')')
  
      if first == -1 or last == -1:
          # no max length specified
          return -1
  
      maxnum = int(tform[first+1:last])
      return maxnum